Figure 3-29.--LVDT quadrature oscilitator.

charged positive. The noninverting integrator IC3-1 will

core from its null position causes the voltage in one

charge C1 so its output goes positive. This positive

winding to increase, while simultaneously reducing the

voltage will cause the inverting integrator IC3-2 to

voltage in the other winding. The difference between the

charge its capacitor C2 and its output will go negative.

two voltages varies with linear position.

This negative voltage will discharge C3. This will con-

tinue until C3 is charged negative and then reverse,

LVDT Demodulator Card

causing the circuit to oscillate. The zener diodes clamp

the output and stabilize the amplitude so the output

The LVDT demodulator card supplies a constant

voltage is a stable 6.5 volts ac.

voltage ac excitation to the LVDT primaries and con-

verts the pitch and roll LVDT amplitude and phase

signals to a variable dc voltage. This is accomplished in

LVDT Demodulator

three separate circuits: the LVDT oscillator and the pitch

and roll demodulators.

The pitch and roll LVDT demodulator are identical

except for their gains. They are called phase sensitive

LVDT Oscillator

demodulators. The input to the demodulator is a vari-

able-voltage, variable-phase signal from the LVDT. This

The LVDT oscillator consists of a quadrature oscil-

signal is full-wave rectified and filtered and its output

lator and a power amplifier. The quadrature oscillator is

polarity is positive for signals out of phase with the

used to generate a constant-amplitude, constant-

reference and negative for signals in phase.

frequency sine wave. The power amplifier is a low-

output-impedance driver used to power the LVDT

Servo Amplifiers

primaries and the pitch and roll demodulator diode

switches.

The pitch and roll servo amplifier circuit cards are

identical except for the gains and servo compensation.

To understand the operation of the quadrature

Three inputs are summed into amplifier A1: LVDT,

oscillator, assume capacitor C3 of figure 3-29 is initially

Figure 3-29.--LVDT quadrature oscilitator.

3-20